In such a burner fuel gas is mixed, before combustion in the burner, with air in a plenum chamber.
The fuel gas is usually supplied from a main while the air is supplied by a fan.
To prevent incomplete combustion of the gas and the production of poisonous carbon monoxide gas, the volume flow rate of air is usually intended to be maintained in excess of the rate theoretically necessary for full combustion of the gas. Typically this excess amounts to 30%, and the burner is then said to be operating with 130% of the stoichiometric air requirement or, for brevity, "at 130% aeration".